1. Field of the Invention
The present invention, in general, relates to a method of operating a navigation system for a vehicle and to a navigation system for a vehicle. More specifically, the present invention relates to a navigation system that provides guidance along a given route and is capable of calculating an advantageous return route to the original route if the vehicle turns off or deviates from the original route.
2. Related Art
In general, the typical task of a navigation system is to guide the driver of a vehicle to a destination on the shortest or the fastest path. Yet for some applications, it is not only important to reach the destination, but also to travel along a predetermined route or path. A good example for such an application is a circular trip or tour, on which several destinations are to be reached. On a circular trip, the starting point and the destination are generally located in close proximity to each other. A navigation system would typically search for the direct path between the starting point and the destination, and guide the driver along this path. With such a system, the guidance along a circular trip that passes by some interesting points, e.g., a monument or a castle, or uses particularly pleasurable road sections, e.g., along a lake, is not possible.
For enabling the guidance along a circular trip, conventional navigation systems may be provided with a list of waypoints. The navigation system then provides guidance in such a way that the waypoints are passed one after the other. A waypoint is marked as reached as soon as the distance to the waypoint becomes smaller than a predetermined value. With such a system, the driver is always guided to the next waypoint that has not yet been passed. Particularly in situations where the driver has left the pre-calculated route, this can be disadvantageous, as the system may guide the driver back to a point which he has not yet passed, even though he has already traveled a fair distance in the direction of the circular trip. Basing the navigation on a round trip on fixed waypoints that have to be passed may thus lead to unfavorable route guidance.
Further, conventional navigation systems may include a function to detour a section of a given route (e.g., in the event of a traffic jam). For returning to the original route, a return point is determined on the original route such as an intersection that has not been passed and is nearest to the current position of the vehicle. A route between the current position and the return point is then searched by minimizing cost, such as traveling time or distance. Additionally, the systems may also search for a new route leading directly from the current position to the destination. Both of these features are disadvantageous when turning off a guided route or when traveling on a circular tour, as directly going back to the guided route may involve turning around and traveling back on the same road section, and directly traveling to the destination is not desired. These conventional systems are in particular not suited for guiding the driver back to a particular road section that the driver wants to travel along, e.g., a particularly scenic road section.
Accordingly, there is a need to provide a method of operating a navigation system that results in an enhanced route guidance along a given route, and to provide a navigation system for a vehicle that is capable of providing such an enhanced route guidance.